Flirting

I have been with a wonderful man for a tumultuous three years and am just now fully digesting the depth of ADD's affect on our interaction.  We are dating long distance but, because we both work shift, end up spending more time together than the average couple.   He has a huge sense of play and I love it.  Relationship wise the ADD has made it quite a roller coaster ride as I strive to understand.  He, on the other had refuses to believe he's ADD and will not go for testing.  He is also dyslexic (formally diagnosed as a child) and can't stomach the idea of another "criticism" of who he is. I love this man for all the wonderful sides to his personality but am in danger of jeopardizing our future because I can't stretch my mind to accept flirting as symptomatic.  I would love to hear some feedback from other people as well as comments on setting boundaries in this area. 

I know this man loves me.  I can feel it and see it in a million different  and unusual ways but he makes light of our relationship and flirts with fb friends, most of whom he's dated.  He maintains it's nothing and I believe he believes it.  I don't feel he is taking it further and he is genuinely affronted to think I would think he's not capable of being monogamous.  When I try to explain my position he feels attacked because in his mind he truly has no intention taking it further.  I have tried to explain the concept of emotional infidelity but again because he genuinely doesn't feel it, he can't understand.  After three years he just now mentions me by name on his fb blurbs.  I get, when he's been in and out of relationships for so long, that he's private about ours.  He has articulated that he doesn't want people to know if another one goes south.

I have tried to explain that if he needs a lot of freedom to be himself he needs to create and atmosphere where I feel secure enough to let him fly.   I am more than prepared to accept that his behaviour is going to be different than the norm and truly enjoy his quirks and idiosyncrasies.  My own limitations are making it impossible for me to find my through this issue. 

I am having difficulty deciding how much of this is ADD affected and how much is just him being disrespectful.  I did ask him why he flirts and got the "I don't know" response.  I believe he doesn't know.  I also asked him if he could ever see himself having more traditional conversations and just not flirting and he said yes.

I'm pretty confused on this issue and am looking for clarity.  I know flirting with other people does not fit within my values but neither does lack of forgiveness.